Environmental concerns and recent increases in the cost of fuel have highlighted a need for fuel efficient vehicles. Since pneumatic tires significantly impact fuel efficiency of vehicles, one way of addressing this need for fuel efficient vehicles is through improvement of pneumatic tires.
Typically, a pneumatic tire includes an inner liner. As part of a pneumatic tire, the inner liner functions as a bladder, which prevents gas from leaking out of the pneumatic tire thereby maintaining tire pressure within the pneumatic tire.
As tire pressure in a pneumatic tire decreases, so does fuel efficiency. Technically, a pneumatic tire's ability to maintain air pressure is related to the permeability of its inner liner. Permeability measurements determine how much permeate (typically air) penetrates the inner liner in a specific time, dependent on the type of permeate, pressure, temperature, and thickness and surface area of the inner liner.
The inner liner is typically formed from a halogenated rubber composition, most often a halogenated butyl rubber compound. The halogenated rubber compositions used to form inner liners have changed very little over the past 50 years. Despite having relatively low permeability compared to inner liners formed from materials used in the distant past, inner liners formed from halogenated butyl rubber compounds still allow gas to permeate out of pneumatic tires, which causes a decrease in tire pressure over time. That is, although inner liners comprising halogenated rubbers have low permeability relative to many other polymeric materials, i.e., they function fairly well to prevent gas from quickly leaking out of pneumatic tires, improvements are still required to decrease the permeability of tires and subsequently minimize decreases in tire pressure over time to improve fuel efficiency.
Further, inner liners comprising halogenated butyl rubber may also exhibit hysteresis loss, i.e., a loss in resiliency, which leads to an increased rolling resistance and decreased fuel efficiency. To improve physical properties, like hysteresis loss, fillers are typically compounded into the halogenated rubbers which are used to form inner liners. The use of fillers increases the density and thus the weight of the inner liner, which, in turn, decreases the fuel efficiency.
In an attempt to solve these problems created by the permeability and resiliency of materials typically used to form inner liners, alternative materials have been suggested. However, materials suggested up to this point do not have all of the physical properties required of an inner liner, such as temperature resistance, or further require changes to the pneumatic tire assembly, which impact cost.
Accordingly, there remains an opportunity to develop an improved inner liner which is significantly impermeable, resilient, temperature resistant, and light weight.